Unlicensed wireless communications systems are required to comply with FCC part 15 rules. These rules limit the bandwidth of operation for frequency hopping systems, such as Bluetooth™ (BT) or HomeRF, resulting in limited system throughput and capacity per radio transceiver. Bluetooth™ is a trademark/service mark of Telefonaktiebolaget LM Ericsson, of Stockholm, Sweden, for telecommunication equipment, computer communication equipment, including radio modems; and telecommunication and computer communication services.
In order to enhance the capacity of a wireless access point (AP), it is possible to incorporate multiple radio transceivers into a single physical AP. In this case, each radio transceiver operates independently of the others inside the same AP. In frequency hopping systems, a radio transceiver will hop in a pseudo-random manner among a number of channel frequencies, using only one channel frequency at a time, e.g., BT hops in a pseudo-random manner among 23 or 79 channel frequencies, depending on regulations governing various geographic regions.
In multi-transceiver AP prior-art, each radio transceiver hops using a different pseudo-random sequence, selecting the next transmission channel frequency independently from the other transceivers. Occasionally two or more of the transceivers in the multi-transceiver AP will select the same channel frequency, resulting in a channel frequency collision. In the event of such a channel frequency collision, the multiple transmissions on the same channel frequency will totally corrupt each other, which will result in none of the colliding transmissions being able to be correctly received and decoded.
The known prior art does not attempt to avoid this kind of collision, but rather relies on error recovery techniques to prevent loss of data integrity, such as backward error correction schemes to subsequently recover the corrupted data. Any unsuccessful transmission will result in the generation of a negative acknowledgements (NACK), which is sent back to the AP. On receipt of such NACKs, the AP will re-transmit the corrupted data, allowing it to be fully recovered. Such prior art systems rely on the fact that channel frequency collisions are rare, and that by the time of re-transmission each AP transceiver has hopped to new, independently selected channel frequency where repeat collision is unlikely, due to the pseudo-random nature of the hopping process. Thus, prior art systems use random hopping and repeat transmissions to provide robust operation. The effect of collisions is loss of system performance: reduced throughput and increased delay.
U.S. Pat. No. 5,410,538, for Method and apparatus for transmitting signals in a multi-tone code division multiple access communication system, granted Apr. 25, 1995 to Roche et al., describes multi-tone CDMA and OFDM, and is related to specifics of design and implementation of this modulation technique.
U.S. Pat. No. 5,481,481 for Automated diagnostic system having temporally coordinated wireless sensors, granted Jan. 2, 1996 to Frey et al., describes a tester for diagnosis of a distributed system. The tester coordinates inputs from loggers at each of the disparate components of the system.
U.S. Pat. No. 5,548,582 for Multicarrier frequency hopping communications system, granted Aug. 20, 1996 to Brajal et al., describes a multi-carrier FH system and signal processing techniques for decoding the transmissions using Fourier Transforms.
U.S. Pat. No. 5,781,536 for Allocation method and apparatus for reusing network resources in a wireless communication system, granted Jul. 14, 1998 to Ahmadi et al., describes a system where multiple WLAN access points at different geographical locations have central resource coordination to allow effective distribution of resources among the access points according to demand.
U.S. Pat. No. 5,790,587 for Multi-band, multi-mode spread-spectrum communication system, granted Aug. 4, 1998 to Smith et al., describes a specific system which uses TDMA, CDMA and FDMA.
U.S. Pat. No. 5,797,099 for Enhanced wireless communication system, granted Aug. 18, 1998 to Ejzak et al., describes a system with coordination between AMPS (analog voice) and CDPD (packet data) services.